Wet-cell Battery Care and Feeding

Posted: September 1, 2014

By: Deane Hislop

Batteries are among the most critical components on a powerboat. Almost all of the onboard systems depend on some form of electrical power for their operation, making battery failure a situation to avoid at all costs. Even high-quality batteries have a finite life expectancy and must be replaced periodically, so the challenge is to use them as long as possible and get your money’s worth.

Ten years ago when outfitting Easy Goin’, we decided on a bank of traditional wet-cell, deep-cycle batteries for the house power. At the time, they provided the best bang for the buck (and in my mind still do). Those same batteries are still providing optimum performance and reliability. While these batteries need more care and feeding than other types of batteries, a well-maintained, quality wet-cell battery will typically provide years of service at low cost.

Safety First

When working with wet-cell batteries, it’s always important to wear protective clothing and hand and eye protection. Keep flames, sparks or metal objects away from the batteries. Use insulated tools. Do not smoke near the batteries and have a solution of baking soda and water available to neutralize an acid spill.


Batteries need to be kept clean and dry. A solution of baking soda and water and a wire brush is used to clean the battery tops and terminals. Before starting, make sure all the vent caps are properly seated to ensure no baking soda solution enters the battery. Apply the solution to the terminal connections and surface of the battery to neutralize corrosion and acid that may be on top of the battery. When done, rinse the top of the battery with water and use paper towels to dry the top of the battery. Once it is dry, ensure the terminal connections are tight, but be careful not to over torque, because doing so could cause terminal breakage. On the other hand, loose connections can cause high resistance and terminal meltdown. Once the connections are properly tightened, apply terminal protection such as an anticorrosion spray or a silicone gel to the terminal posts, to reduce corrosion.


A very important process in the caring of deep-cycle flood-type batteries is watering. A deep-cycle battery will lose water/electrolyte during the charging process, so it’s important to replenish the lost water. The frequency you will have to add water is dependent on your use. It’s best to monitor the levels in your batteries every couple of weeks to determine the frequency for your application. Only distilled water should be used, as it does not contain any impurities that will impact the life and performance of the battery. Never add acid or electrolyte to the cells, because it will cause a chemical imbalance.

To check or add water, remove the vent cap, add water and reinstall the cap; make sure it’s on tight. Water should only be added when the battery is fully charged. Add it to a level of 1/8 inch below the bottom of the fill well, being careful not to overfill the cell.

Never let the electrolyte levels go below the top of the plates, because it will cause harm to the plates and will also affect performance.

Never add water to a discharged battery if the electrolyte is visibly above the plates. If the cell plates are exposed, add water to discharged batteries to a level just above the plates, charge the battery and then top off to 1/8 inch below of the fill well.

Charging and Equalization

With today’s preprogrammed battery charges, charging is made easy. Prior to charging, however, make sure the charger is set on the flood battery setting for proper charging levels, the vent caps are securely in place and proper ventilation is in place, to prevent gas buildup.

Battery equalization is an important part of any flood-type battery maintenance program. Equalization is an overcharge that is conducted on flood lead acid batteries after they have been fully charged. The equalizing process will mix the electrolyte to address imbalanced cells and reduce stratification.

It’s important because it reverses the buildup of negative chemical effects, such as stratification, a condition where acid concentration is greater at the bottom of the battery than at the top. If the electrolyte is not mixed routinely, the heavier sulfate particles will sink to the bottom of the cell, which increases the density of the electrolyte and causes the bottom of the plates to corrode.

Equalizing also helps remove sulfur crystals that might have built up on the plates. If left unchecked, this condition, called sulfation, will reduce the overall capacity of the battery. Some battery manufacturers recommend equalization be conducted every 30 days.

The equalization process is performed by putting the battery charger setting on equalization. What will happen at this point is your batteries will begin to release hydrogen and oxygen gases. Don’t be alarmed, as this is normal. At this point, begin measuring the gravity level of each cell with a hydrometer until it ceases to rise, then stop the equalization charge. Some battery chargers have a pre-programmed equalization mode that schedule equalization every 30 days. Always consult your battery manufacturer’s charging specifications for its recommendations.

Never attempt to equalize valve-regulated batteries such as AMG or gel-type batteries.

Properly maintained flood batteries will continue to operate at peak levels of optimum performance and reliability for years, regardless of their application.

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